Optical glass



' primarily consists of 1.8.203, ThO B OPTICAL GLASS Walter Getfcken, Mainz, Germany, assignor to *Ienaer Glaswerk Schott & Gen., Mainz, Germany, a German corporation No Drawing. Filed May 23, 1958, Ser. No. 737,220 Claims priority, application Germany May 23, 1 9 57 13 Claims. (Cl. 106-54) The present invention relates to optical glass which T8205, ZrO W0 alkaline earths, ZnO, and SiO and has a very high refractory index as well as a very high fi-value.

Similar glass known prior to this invention had, for example, the following composition:

a Percent LnzO; 19. 21. 4

Such glass had'a refractory index of or l. 762 at a v-value'of 46.0 01 48.0, respectivelylfConsidering its excellent optical properties, such contained a relatively small amount of valuable rawmaterials. However, it had the disadvantage that it was very diflicult to melt larger batches of this glass because of its inclination to crystallize. v

According to the present invention, it has now been found that the danger of crystallizationmay be avoided, and that the optical properties of the glass may be even further improved by reducing the content of the men tioned bivalent oxides below the former minimum limit of 28%, and by making it between 10 to 18% by weight, of which a maximum of 7% should be taken up by the group of alkaline earths, while the remainder should consist of ZnO and 010. The upper limit of La O and T110 should then be increased accordingly. The 810; content should also be decreased and should not exceed 6%, and in its stead the upper limit of the boric acid content should be increased to 30% by weight.

The glass according to the present invention is preferably divided into two groups, one of which'has a refractory index between 1.770 and 1.805, while'the other has arefractory index above 1.805.

The compositions of these two groups of glass are, I

according to the invention, as follows:

TABLEI I 1. i1d=1.7701.05 2 111121.805

Percent Percent 1.11 0 24 to 33 24 to 33. T1101 16.510 25.5 16.5 to 25 5 BzOa-l-SiOa 23.5 to 30 19.5 to 30 S10 6 6. Bivelent Oxides 10 to 18 10 to 18 CaO+Sr0+BaO 7 5. Cd0+ZnO 3 to 1 9.5 to 15. 2110 3 to 10 0 to 10. T3201 OtoR 5m 13 W01- 1 to 10 WOrl-TQ O 15.

2,971,854 Patented Feb, 14, 961

The glass in group nd 1.805 has a certain similarity to the glass described in the published German patent application No. 1,003,410 (inventor De Paolis) which defines a glass having an nd-value of 1.82 to 1.89. However, the glass according to the invention differs from the glass in the mentioned patent application by its lower content in the very costly tantalum oxide which is necessary therein for the purpose of stabilization if the bivalent material consists of H210. However, particularly in a glass with an nd-value of more than 1.82, a higher content in Ta O has a very unfavorable effect since it reduces the v-value.

In the glass according to the present invention, the stabilization will be attained by means of the relatively high content in ZnO+CdO in the presence of substantially equal constituents inThO and 1.11 0,. The abovementioned upper limit of the T21 0, content will not even be required if the ZnO and CdO content is suitably selected. Also for reasons of economy, the amount of Ta O applied will usually be made in the vicinity of the mentioned lower limit so that the content in tantalum oxide in the group with an nd-value of 1.77 to 1.805 will be below 3.5%, while in the group with an nd-value of more than 1.805 it is preferably made less than 10%.

The contents in ZiiO and CdO should theii amount that alkaline earths should be less than 6%.

Thus, the following table of components'will result:

TABLE 2 1..nd=1.77i to 1.805 2. nd=1.805

. Percent Percent La o V 24 to 33 24 to 33. Th0; 16.5 to 25.5 16.5 to 25.

BzOa-l-SiOg 23.5 to 30 19.5 to 30.

SiOq 6 6. Bivalent oxides 10 to 18 10 to' 18. OaO+SrO+BaO 6- 5. CdO+Zn0 5 to 15 9.5 to 15. ZnO 3 to 10 0 to 10; TazOrn 0 to 1 5 5 to 10. W03"- 1 to 10.

An addition of W0 also favorably afiects the stability of the glass if it belongs to one of the groups with a lower refractory index, although it is advisable to keep it at an amount of less than 1.5% so as not to reduce the v-value. Also, in all cases it is possible to provide an addition of ZrO at an amount of up to 6%. As usual, the WO content may be partly replaced by M0 and also the Ta O content by Nb O In the group with the lower refractory index, the CdO- content should preferably not exceed 5% ,"While in the group with the higher refractory index, thelZnoacontent should not be reduced to less than 3% if a' very high 11 should be desired. Also an addition of L1 0 of .up to 1% may be provided.

'If maximum i-values are to be attained, it is advisable not to reduce the sum of La203+ThO to less than 4 9%. The production of the glass according to the present invention is carried out in the usual manner in a platinum crucible. La O SiO CdO, ZnO, ZrO Ta O and W0; are preferably added to the mixture in the form of oxides, while BaO, SrO, and Th0 are added in the form of nitrates and CaO in the form of a carbonate. The

' glass mixture melts very easily, and it is therefore not 3 more than 0.5%. The glass composition is preferably stirred as usual until it has a syrupy consistency, which occurs at a temperature of approximately 950, whereupon the glass is poured as usual into a preheated iron mold in which it is made stain-free by slow cooling in a cooling oven. Even large batches of this glass may be melted without crystallization. The glass finally attained is practically colorless, provided the purest kind of raw materials have been used.

The following compositions according to the invention excel by unusually favorable optical properties at an extremely low content in the costly tantalum oxide.

Percent 178.203. 27 to 20.... 27 to 29. T1101 20 to 23 20 to 23. B203" 27 to 30 23.5 to 27. BaO+SrO+CaO 4 to 6 4 to 6.

O 4 t 6 4 to 6.5. ZnO-l-CdO 8 to 10 to 15.

03-- 0.5 to 1.5 0.5 to 1.5. T3205. 0 t0 2 t0 3 5. ZrOz.. 3 to 5 TABLE 3 No 15 16 17 V 18 19 20 least 1.77 and consisting essentially of the following composition:

. Percent La o 24 to 33 Th0, 16.5 to 25.5 B 0 +SiO 19.5 to 30, in which S102 I Bivalent oxides 10 to 18, in which v CaO-l-SrO-l-BaO 7 CdO-l-ZnO 3 to 15, in which ZnO 0 to 10 T3305 010 13 W0 0to 10, in which Ta O +WO 15 tially of the following composition:

2. An optical glass as defined in claim 1 having a refractory index of 1.77 to 1.805 and consisting essen- Percent La O 24 to 33 Th0: 16.5 to 25.5 B O +SiO, 23.5 to SiO- 6 Bivalent oxides 10 to 18 CaO+SrO+BaO 7 CdO-i-ZnO 3 to 15 ZnO 3 to 10 T3205 0 0'8 3. An optical glass as defined in claim 1, having a refractory index of M51805 andconsisting essentially of the following composition:

4. An optical glass as defined inclaim 2 having a refractory index of nd=1.77 to 1.805 and consisting essentially of the following composition:

Percent. La O 24 to 33 Th0, V 16.5.to 25.5 B Q +SiO 23.5 to 30 SiO 6 Bivalent oxides 1010 18 CaO+SrO+BaO 6 CdO-i-ZnO 5 to 15 ZnO 3 to 10 Ta O r, 0 to 3.5

Although my invention has been illustrated and de-' scribed with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments or to the 5. An optical glass as defined in claim 3 having a refractory index of nd;1.805 and consisting essentially of the following composition:

'Pereent Lap, 24 to 33 Th0, 16.5 to 25.5 j. BaQsrlfiQa 1 30 Bivalent oxides 10 to 18 CaO+SrO+BaO 5 CdO-l-ZnO 9.5 to 15 0 to 10 T3205 5 to 10 W0 1 to 10" 6. An optical glass as defined inclaim 4, having a 7 content in WC, up to 1.5%.

7. An optical glass as defined in claim 6,-having a' V 1. An optical glass havingian index-of refraction ofat content in ZrO up to 6%.

8. An optical glass as defined in claim 4, having a content in CdO of less than 5%.

9. An optical glass as defined in claim 5, having a content in ZnO of at least 3%.

10. An optical glass as defined in claim 9, wherein the sum of La O +ThO amounts to at least 49%.

11. An optical glass as defined in claim 7, consisting essentially of the following composition:

Percent La O 27 to 29 ThO 20 to 23 B 27 to 30 BaO+SrO+CaO 4 to 6 ZnO 4 to 6.5 ZnO+CdO 8 to 10 W0 0.5 to 1.5 Ta O 0 to 2 ZrO 3 to 5 12. An optical glass as defined in claim 6 consisting 13. An optical glass having a refractory index of nd=1.805 and consisting essentially of the following composition:

Percent B 0 21.3 La O 27.7 T 21.3 ZnO 4.9 CdO 5.4 BaO 3.8 W0 1.2 T3205 ZrO 2.0

References Cited in the file of this patent UNITED STATES PATENTS 2,241,249 Eberlin et al May 6, 1941 2,434,149 De Paolis Jan. 6, 1948 2,787,554 De Paolis Apr. 2, 1957 FOREIGN PATENTS 615,286 Great Britain Jan. 4, 1949 

1. AN OPTICAL GLASS HAVING AN INDEX OF REFRACTION OF AT LEAST 1.77 AND CONSISTING ESSENTIALLY OF THE FOLLOWING COMPOSITION: PERCENT LA2O3 - 24 TO 33 THO2 - 16.5 TO 25.5 SIO2 - <6 BIVALENT OXIDES - 10 TO 18, IN WHICH CAO+SRO+BAO <7 CDO+ZNO - 3 TO 15, IN WHICH ZNO - 0 TO 10 TA2O5 - 0 TO 13 WO3 - 0 TO 10, IN WHICH TA2O5+WO3 <15 